Pop philosophers from U2 to Queen Latifah have long coveted unity — harmony among people, inspired by music. Arcade Fire, today’s reigning big-message rock band, bring more cynical tidings on their intrepid, uneven, and very long (75 minutes) fourth album, Reflektor. Whether talking religion or pornography, frontman Win Butler sees a spy-vs.-spy world — us and them trapped in colliding echo chambers. The song titles hint at this bleak idea: ”We Exist” and ”Normal Person” root reflexively for the outcasts, while ”Supersymmetry” and ”Reflektor” suggest that the alliances we form amount to little more than group selfies.

Butler & Co. have always known whose side they’re on when it comes to existential questions about war or suburbia. But here, with LCD Soundsystem mastermind James Murphy as their new producer, they sound as separatist as they feel. It’s not a rebrand of Murphy’s beloved, now-dead dance-rock outfit — although LCD fans will get a tingly feeling from the album’s first single, the champagne-bath title track. Arcade Fire were already locking into retro-German grooves on their last effort, 2010’s Album of the Year Grammy winner The Suburbs; Murphy tunes them up for the autobahn, plumping the bass guitar and making the beats bubbly. He also opens them up to joyrides like ”We Exist,” with its son-of-”Billie Jean” bass line and glassy guitars straight from Blondie.

Reflektor indulges dodgier impulses, too, tossing together spongy dub and steel-wool punk, sometimes in one draggy track. (Songs regularly stretch past six minutes.) ”Joan of Arc” honors the hipster saint’s ”vision” with a sultry, rhythm-first drive that flowers prettily. But the band loses the groove on experiments like the rawk tantrum ”Normal Person” and the primitivist reggae interlude ”Flashbulb Eyes” — which asks, in all seriousness, ”What if the camera do really take your soul?”

This rumpus seems particularly gratuitous in light of sleeker, more evocative fare like ”Porno,” an ominous synth ballad that mercifully abstains from musing on how sex videos harm the human spirit. But Butler can’t resist giving unsolicited advice, as on ”Here Comes the Night Time”: ”Now the preachers they talk up on the satellite/If you’re looking for help, just try looking inside.” Thankfully the band itself, righteously goosed by Murphy, doesn’t insist on such stern self-reliance. B